Systems for measuring speed and/or length of moving objects are needed for various applications. As an example, a system for measuring the speed and length of a yarn may be needed for a yarn producing machine to measure the output of the machine. Conventional systems for measuring speed and/or length of moving objects include physical contact-type measuring systems and optical measuring systems.
Conventional physical contact-type measuring systems typically use a roller that contacts a moving object that is being measured. The rotation of the roller is then measured using a rotation sensor to calculate the speed of the moving objects. From the speed calculation, the length of the moving object can be derived for a certain time interval.
A concern with conventional physical contact-type measuring systems is that the roller introduces resistance, which can affect the performance of the machinery that is moving the object. Another concern is that these systems are subject to structural failure due to the mechanical nature of the roller. Still another concern is that the contact of the roller with the moving object may introduce contaminations, which may degrade the quality of the object
Conventional optical measuring systems typically use an image sensor array with active photosensitive elements to electronically capture a surface of a moving object as successive frames of image data. When capturing the image frames, all the active photosensitive elements of the image sensor array are used to capture an individual image frame. Thus, the captured image frames are of the same size. These image frames are compared to track displacement of features in the image frames. The feature displacement can then be used to calculate the speed and/or length of the moving object.
A concern with conventional optical measuring systems is that comparing image frames to track displacement of features requires a significant amount of data processing. Thus, these conventional optical measuring systems are limited by their data processing capability and/or the speed of the moving object being measured. Thus, a potential solution requires the use of fast processors, which translates into increase in system cost. Another concern is that these systems are not very reliable when the width of the moving object being measured is thin, especially when high speeds of the moving object are involved.
Thus, there is a need for a system and method for optically measuring the speed or length of a moving object, which can produce reliable results while minimizing cost.